This invention relates to chuck assemblies for tool bits and, more particularly, to a quick release chuck adapted to prevent undesired axial extraction of a tool bit such as a drill from the chuck assembly. The invention enables users to change tool bits in the chuck assembly quickly and easily.
Tool bits include tools used for drilling and for driving fastener devices such as screws, nuts and bolts, and other work elements requiring rotational motion. The American National Standards Institute has a specification, own as ANSI B107.4-1982, which pertains to the driving and spindle ends for portable powered and hand held machines using the tool bits. Tool bits in accordance with the specification have a hexagonally configured shank with a circumferential groove formed into the shank. The circumferential groove has a flat, bosom portion disposed between two radiused shoulder portions. The standard reflects the long term and pervasive use of such tool bits and the large inventory of tools available.
It has long been recognized that the ability to quickly change tool bits in the spindle of a power source is an advantageous feature. Numerous examples exist in the art of quick release tool chucks. An example of one such quick release chuck apparatus is described in U.S. Pat. No. 4,692,073. The quick release chuck disclosed therein includes a spring biased sleeve disposed on a spindle having an inclined cam surface disposed against a single ball.
The ball in turn applies normal and tangential forces against a groove in the shank of the tool bit to hold the tool bit in a bore. The sleeve is urged into contact with the ball by a compression spring disposed between the spindle and the sleeve. A ring secured to the spindle limits the movement of the sleeve in one direction, and the compression spring and the spindle limit the movement of the sleeve in the opposite direction.
U.S. Pat. No. 4,692,073 addresses objectionable end play caused by the presence of the flat, bottomed portion of the circumferential groove in the tool bits. However, construction of devices taught by the patent require maintenance of extremely tight manufacturing standards with respect to the radius of the ball and both the radius of the radial bore it travels in and the radius of the radiused shoulders in the groove which it abuts against. The ramped sleeve which is used to apply normal and tangential forces to the ball can allow the ball to be forced out of the retaining position by a large outward axial force applied to the tool. A large outward axial force can occur, for example, where the tool bit is a drill bit being removed from a freshly drilled bore. Use of a single detent ball can also result in a nonconcentric orientation of the tool.
U.S. Pat. No. 5,013,194 discloses a chuck assembly for a tool bit including a spindle with a quick release mechanism adapted to prevent undesired axial extraction of the tool bit from the spindle. The tool bit includes a shank portion with a circumferential groove in accordance with the ANSI standard. A longitudinally extending bore is provided in the spindle for receiving the shank portion of the tool bit. Opposing radial bores communicate with the shank receiving bore. Detent balls are disposed in the opposing radial bores. The shank is retained in the bore by the balls, which extend from the radial bores into the shank receiving bore and against the circumferential groove of the shank.
The detent balls' disposition in opposing positions around the shank help center the shank. A spring biased shoulder is urged against the balls, locking them against a retaining face. Attempted axial extraction of the tool bit from the bore, without release of the detent balls, pulls the balls against a retaining face, thereby producing an opposite tangential force to the axial retraction force. The responsive tangential force prevents extraction of the tool bit from the shank receiving bore.
The existing quick change chuck assembly designs employ relatively bulky locking mechanisms which result in the assembly protruding beyond the nose of the standard drill chuck in a manner which may cause interference during use of the chuck assembly. Further, these prior art chuck assemblies have an outer diameter wider than the standard chuck. The operation of the systems also requires the user to manipulate a portion of the adaptor while inserting the tool bit. As a consequence, these systems can sometimes be bulky or cumbersome for use in particular applications. Additionally, the prior art systems require the production and assembly of many small parts, which increases the difficulty and cost of producing the quick change chuck assembly.